1. Field of the Invention
The present invention relates generally to inductors of a laminated or stacked-layer structure including self-inductive inductors and mutual-inductive inductors. More particularly, the present invention is concerned with composite winding type stacked-layer inductors including self-inductive inductors and mutual-inductive inductors such as transformers.
With the phrase "composite winding type laminated or stacked-layer inductor", it is intended to mean an inductor of such a structure which includes plural sets of electric conductor windings formed in parallel through a layer stacking or layering process by making use of a conventional printing method, vapor phase methods such as sputtering, evaporation and CVD methods or others. Further, with the term "inductor", it is contemplated to mean an inductor realized by a single winding or by a plurality of electric conductor windings connected in series to form a self-inductive inductors or in parallel to form a mutual-inductive inductor or transformer. The inductor of concern can be used not only alone but also in combination with the inductor(s) according to the invention or other inductor(s) known heretofore to thereby form transformers or the like. Besides, the inductor can find a variety of applications such filter circuits, composite LC-circuit chips, composite LR-circuit chips, composite LCR-circuit chips and other various integrated circuits incorporating other circuit elements such as diodes, transistors, thermistors and/or the like. To say in another way, the composite winding type stacked-layer inductor according to the present invention can be employed for any applications which require the inductor as the indispensable circuit constituent. Thus, the inductor according to the invention is never limited to the independent utilization thereof.
2. Description of the Related Art
In the Japanese Patent Publication No. 39521/1982, Japanese Patent Application Kokai No. 22304/1984, Japanese Patent Publication No. 14487/1988 and U.S. Pat. No. 4,322,698 filed in the name of the inventors of the present application, there are proposed such an integrated structure of a sintered stacked-layer inductor in which magnetic ferrite layers and coil-forming strip-like conductor layers are deposited or stacked alternately with each other and subsequently sintered into an integral structure. In the stacked-layer inductors according to these preceding proposals, a plurality of printed conductor strip layers each having a length corresponding to about a half turn are mutually interconnected byway of edge portions of the printed ferrite magnetic layers intervening the conductor strip layers so that the conductor strip layers each of abut a half turn cooperate to constitute a coil wound in the direction in which the layers are stacked, whereon the whole coil thus obtained is then sintered to an integral structure.
In the following, the prior art techniques relating to the present invention will be described in some detail by referring to FIGS. 83 to 112 of the accompanying drawings for having a better understanding of the invention. Parenthetically, in the stacked-layer inductor manufacturing process, it is commonly practiced to implement simultaneously a plurality of stacked-layer inductors on a single delamination-easy (i.e. easily removable or separable) substrate having a large surface area. However, the following description will be made on the assumption that a single stacked-layer inductor is to be manufactured only for convenience of the description. In the drawings mentioned above, the figures labelled with (a) show plan views with those labeled (b) showing sectional views.
Referring to FIGS. 83 to 97 showing a first prior art technique, an easily strippable or delamination-easy substrate (not shown) having a polyester layer (preferably a polyethylene terephthalate layer) deposited over a surface of a substrate material (such as aluminium and the like) having high flatness and smoothness is printed with an magnetic ferrite layer 1 having an electrically insulating property and a magnetic permeability, which layer may have a surface deposited with an electrically insulating coating. Next, printed on the magnetic ferrite layer 1 in such a pattern as illustrated in FIG. 84 is a ferrite layer 2 for compensating for a print offset (difference in the thickness) which would otherwise be produced through the printing process, being then followed by the printing of a coil lead-out conductor strip 3 as shown in FIG. 85. Subsequently, a magnetic ferrite layer 5 is printed over a right half so that a start end portion 4 of the coil lead-out conductor strip 3 remains exposed, as shown in FIG. 86. Next, an electrically conductive strip 6 for forming about a half turn of the coil is printed so as to be connected to the start end portion 4, as shown in FIG. 87, which is then followed by the printing of a magnetic ferrite layer 7 over a left half of the surface in such a manner that an end portion of the coil forming conductor strip 6 remains exposed. Subsequently, a coil forming conductor strip 9 for forming about a half turn of the coil is printed in electrical contact with the end portion 8 of the coil forming conductor strip 6, as illustrated in FIG. 89. Next, a magnetic ferrite layer 11 is printed over the right half with an end portion 10 of the coil forming conductor strip 9 being left as exposed, as shown in FIG. 90. At a next step, a coil forming conductor strip 12 is printed for forming about a half turn of the coil in contact with the end portion 10 of the coil forming conductor strip 9, as shown in FIG. 91. Subsequently, a magnetic ferrite layer 13 is printed over the left half with an end portion 14 of the coil forming conductor strip 12 being left exposed, as shown in FIG. 92, being then followed by the printing of a coil forming conductor strip 15 for forming about a half turn of the coil in contact with an end portion 14 of the coil forming conductor strip 12, as shown in FIG. 93. Then, a magnetic ferrite layer 17 is printed on the right half. Through the stacking process up to the step shown in FIG. 92, there are deposited in a stacked or laminated structure the conductor Strips 3, 6, 9, 12 and 15 which cooperate to form a coil of about two tums. For realizing the coil having a desired number of turns, the conductor strip stacking steps similar to those shown in FIGS. 91 to 94, respectively, my be repeated for a corresponding number of times. For convenience of description, let's assume that the layer stacking process is terminated at the manufacturing step shown in FIG. 94. After having formed the coil forming conductor strips corresponding to desired number of turns in general and in the simplified example the two turns, a coil lead-out electrical conductor strip 18 is printed, as shown in FIG. 95. Subsequently, a magnetic ferrite layer 19 is printed over the whole surface, as shown in FIG. 96, whereon the product thus obtained is sintered. Finally, terminals required for external connection are formed by baking or the like method. Thus, a stacked-layer inductor is finished. An equivalent electric circuit diagram of the stacked-layer inductor is illustrated in FIG. 97.
A method of manufacturing a stacked-layer inductor according to another printer art technique is illustrated in FIGS. 98 to 112 of the accompanying drawings. (Concerning this prior art, reference may be made to JP-A-59-22304). These figures show in plan views a process for manufacturing a stacked-layer inductor by making use of a layer stacking technique such as a printing method, a vapor phase method typified by sputtering, evaporation and others. The stacked-layer inductor as illustrated is manufactured by resorting to a printing method.
More specifically, FIGS. 98 to 107 show in plan views a process of manufacturing a composite winding type stacked-layer inductor according to the prior art technique in which the axis of turns of a primary coil winding formed by stacked conductor strips and extending from a point P.sub.1 to a point P.sub.2 is deviated or offset from the axis of turns of a secondary coil winding extending from a point S.sub.1 to a point S.sub.2. The stacked-layer inductor now under consideration is destined to be used as a transformer. On the other hand, FIGS. 108 to 112 show a process of manufacturing a composite winding type stacked-layer inductor having the concentric axes of turns formed by the coil forming conductor strips deposited concentrically, whereby the primary winding forming conductor strips are disposed coaxially with the secondary winding forming conductor strips.
Describing the second prior art method, a magnetic layer 31 of magnetic ferrite or the like material is printed on a delamination-easy substrate (not shown), and then a primary winding conductor strip 32 is printed on the magnetic layer 31 about a half turn, as shown in FIG. 98. An end portion P1 of the conductor strip 32 is lead out to a peripheral portion of the magnetic layer 31. Next, the conductor strip 32 is covered with another magnetic layer 34 except for an end portion 33 of the conductor strip 32, as shown in FIG. 99. Subsequently, a secondary winding conductor strip 35 having a lead-out end portion S.sub.1 is printed about a half turn and simultaneously connected to the end portion 33 of the conductor strip 32 to thereby form a conductor strip 36 of about a half turn. Next, a further magnetic layer 39 is deposited by printing on the conductor strips 35 and 36 with end portions 37 and 38 thereof being left exposed, as can be seen in FIG. 100. At a next step, conductor strips 40 and 41 are printed each about a half turn in contact with the end portions 37 and 38, respectively. Thereafter, a magnetic layer 44 is deposited by printing in such a pattern that the end portions 42 and 43 of the conductor strips 40 and 41 are left exposed, which is then followed by the printing of conductor strips 45 and 46 each corresponding to a half turn in contact with the end portions 42 and 43, respectively, as shown in FIG. 101. Next, a magnetic layer 47 is printed as in the case of the magnetic layer 39, whereby the conductor strip 46 is lead out to the terminal end P.sub.2 on the right side through the medium of a conductor strip 48 while the conductor strip 45 is extended by a conductor strip 49 corresponding to about a half turn, as will be seen in FIG. 102. Next, a magnetic layer 50 is printed in a manner similar to the case of the magnetic layer 44, wherein an end portion of the conductor strip 49 is lead out to a terminal end S.sub.2 on the left side of the stacked layer structure by printing a conductor strip 51, as shown in FIG. 103. Finally, a magnetic layer 52 is printed over the whole surface, as shown in FIG. 104. For implementing the primary coil winding conductor strips or the secondary coil winding conductor strips with a described number of turns, the layer stacking steps shown in Figs, 100 to 101 are repeated a requisite number of times. After having stacked a desired number of the conductor strips, the stacked layer structure is then subjected to a sintering process, whereon electrically conductive paste of suitable types are baked to the lead-out end portions P.sub.1, P.sub.2, S.sub.1 and S.sub.2, respectively. Thus, there can be obtained a stacked layer-inductor chip.
Next, a stacked layer inductor manufactured according to a third prior art method illustrated in FIGS. 108 to 112 will briefly be described. (Concerning this prior art, reference may be made to JP-A-59-22304.)
Describing the third prior art inductor, a magnetic layer 62 is printed on a delamination-easy substrate (not shown), being followed by the printing of a conductor strip 63 on the surface of the magnetic layer 62 for forming a part of the primary coil winding of about a half turn which has a lead-out end portion P.sub.1, as can be seen in FIG. 108. Subsequently, a magnetic layer 64 is printed with a portion of the conductor strip 63 being left exposed, whereon a conductor strip 65 of about a half turn is printed in contact with one end portion of the conductor strip 63, while a conductor strip 66 is printed for forming about a half turn of the secondary coil winding extending from a lead-out end S.sub.1 located on the right side, as can be seen in FIG. 109. Subsequently, a magnetic layer 67 is printed with end portions of the conductor strips 65 and 66 being left exposed, whereon conductor strips 68 and 69 each of about a half turn is printed while making contact with the end portions of the conductor strips 65 and 66, respectively, as shown in Fig. [ 10. Next, after having printed a magnetic layer 70 a conductor strip 71 is so printed as to extend from the exposed end of the conductor strip 68 to the lead-out end portion P.sub.2 located on the left side of the stacked-layer structure, while a conductor strip 72 of a substantially U-like shape is so printed as to extend from the exposed end of the conductor strip 69 to the lead-out end portion S.sub.2 on the right side of the stacked-layer structure, as can be seen in FIG. 111. It will readily be understood that a stacked-layer inductor having a desired number of turns of the winding can be obtained by repeating the layer stacking step shown in FIG. 110 and a subsequent similar step but with the pattern in FIG. 110 is turned by 180 degrees about the axis normal to the sheet a corresponding number of times.
After having completed the stacking o#the layers corresponding to a desired number of tuns, a magnetic layer 73 is printed and then the whole structure is sintered with terminals S.sub.1, S.sub.2, P.sub.1 and P.sub.2 for external connection being formed by baking, whereby a stacked layer inductor chip can be obtained, as shown in FIG. 112.
Further, it has also been proposed to combine two or more inductors in a composite structure for use as a transformer having an intermediate or center tap. To this end, there is known a method of providing a center or intermediate tap 237 exemplified in FIG. 125 in the course of manufacturing process (according to a fourth prior art method) illustrated in FIGS. 116 to 125 of the accompanying drawings or a method of providing a center or intermediate tap 299 as illustrated in FIG. 126 on the way in carrying out the manufacturing process described previously in conjunction with FIGS. 83 to 96 (first prior art method).
Now referring to FIGS. 116 to 125, a magnetic ferrite layer 241 of an electrically insulating material is printed over a whole surface of a delamination-easy substrate (not shown), whereon a conductor strip 243 for forming a primary coil is printed about a half turn on the magnetic ferrite layer 241 and lead outwardly to the left to thereby form a lead-out portion 245, being then followed by the printing of a conductor strip 243' of about a half turn for forming the secondary coil, the conductor strip 243' being lead outwardly to the right to form a lead-out portion 245'. For forming the center or intermediate tap, the lead-out portions 245 and 245' are baked, as described hereinafter, whereon terminal 269 and 273 may be attached externally as shown in FIG. 125 or alternatively the conductor strips 243 and 243' may be connected to each other by printing. The conductor strips 243 and 243' constituting parts of the primary and secondary coils, respectively, are printed, being distanced from each other in the horizontal direction as viewed in the drawings. Next, a magnetic ferrite layer 249 is printed with end portions 247 and 247' of the conductor strips 243 being left exposed, respectively, as shown in FIG. 117. Subsequently, conductor strips 251 and 251' are printed each about a half turn in contact with the end portions 247 and 247', respectively, as shown in FIG. 118. Thereafter, a magnetic ferrite layer 255 is printed with end portions 253 and 253' of the conductor strips 251 and 251' being left exposed, as shown in FIG. 119, in succession to which conductor strips 257 and 257' are printed each about a half turn in contact with the end portions 253 and 253', respectively, as shown in FIG. 120. Subsequently, a magnetic ferrite layer 261 is so printed that the end portions of the conductor strips 257 and 257' are left exposed, as shown in FIG. 121. For realizing the coils each having a desired number of turns, the layer stacking steps shown in FIGS. 117 and 120 may be repeated a requisite number of times. After having completed the stacking of the layers in a desired number, conductor strips 263 and 263' are so printed as to be connected to the end portions 259 and 259' of the conductor strips 257 and 257', respectively, and then lead outwardly to the left and the right to thereby form lead-out portions 265 and 265', respectively, as shown in FIG. 122. Next, a magnetic ferrite layer 267 is printed over the whole surface, as shown in FIG. 123, whereon the stacked-layer structure is sintered. Finally, terminals 269, 271, 273 and 275 required for external connection are formed by baking. Thus, a stacked layer or laminated transformer provided with a center or intermediate tap can be obtained. FIG. 125 shows schematically an equivalent electric circuit diagram of this stacked-layer transformer with the intermediate tap.
Another example of the process for manufacturing a stacked-layer transformer having an intermediate tap (according to fifth prior art method) will be described by making reference to the manufacturing process shown in FIGS. 83 to 99 (according to the first prior art method). In the case of the instant example, an electrical conductor (not shown) to be lead out from the conductor 9 to the right side of the stacked-layer structure is simultaneously printed upon carrying out the step shown in FIG. 89. In this way, an inductor or a transformer having an intermediate tap 299, a primary tap 285 and a secondary tap 295, as shown in FIG. 126, can be implemented.
The stacked-layer transformer having the intermediate tap realized through the layer stacking steps illustrated in FIGS. 116 to 124 suffers from a problem that the width is increased, although the transformer can enjoy an advantageous effect that the thickness is reduced by virtue of the fact that the primary coil and the secondary coil are constituted by the layers stacked in parallel. On the other hand, the stacked-layer transformer with the intermediate tap shown in FIG. 126 in which the primary and secondary coils are realized by stacking sequentially the layers presents a problem that the thickness is increased, although the width of the stacked-layer transformer can well be controlled in respect to the width to an advantageous effect. Thus, none of the stacked-layer transformers described above cannot sufficiently satisfy the requirements imposed for miniaturization as demanded in the field of this art.
In conjunction with the bifilar winding process illustrated in FIGS. 98 to 107 (according to the second prior art method), it is noted that a transformer having an equivalent circuit configuration shown in FIG. 162 can be obtained by providing a lead-out conductor (not shown) which extends from the conductor 41 to the right edge of the stacked-layer structure at the step shown in FIG. 100.
The bifilar winding type stacked-layer transformer shown in FIGS. 98 to 112 is disadvantageous in that the overall thickness is increased because no more than two electric conductors for the coils can be provided in each of the layers. Further, in the case of the bifilar winding type stacked-layer transformer shown in FIG. 163 in which a pair of primary and secondary coils can be realized by stacking the corresponding layers continuously by way of the intermediate tap (c) suffers from a problem that the thickness is increased, although the width of the stacked-layer transformer can advantageously be controlled with regard to the dimension of the width.